1. Field of the Invention
The present invention relates to a composition for inhibiting the expression of one or more target genes in a eukaryotic cell by means of RNA interference, and to the use of appropriate compositions and to a method for inhibiting the expression of one or more target genes in a eukaryotic cell by means of RNA interference.
2. Description of Related Art
The phenomenon known from the literature as “RNA interference” (RNAi) is based on the fact that short RNA molecules (siRNA, small interfering RNA) can interact with messenger RNA (mRNA) in the cell (Literature: Fire A., Xu S., Montgomery M. K., Kostas S. A., Driver S. E., Mello C. C., Nature Feb. 19, 1998; 391 (6669): 744-745). A complex mechanism, which is controlled by enzymes, results in breakdown (degradation) of the mRNA, thus inhibiting the expression of the mRNA and therefore also protein expression (called gene silencing, i.e. switching off a gene or gene inactivation).
Besides siRNA, further small RNA species have been discovered, for example the micro-RNAs (miRNA) or short hairpin RNAs (shRNA), which are likewise able to inhibit protein expression by related mechanisms.
WO 02/44321 discloses the introduction of siRNA into cells in order to inhibit the expression of a gene which occurs naturally in the cells. WO 02/44321 further discloses the introduction of a foreign target gene into a cell. Expression of the introduced target gene can be inhibited by additional introduction of siRNA, which is always derived from the sequence of the introduced target gene, in the expression.
It has emerged that not every sequence is equally suitable for the RNA interference mechanism. Some criteria for the composition of an efficient siRNA have been identified. Reynolds et al. published a selected criteria in Nat. Biotechnol. March 2004, 22(3): 326-330. Electronic publication took place on Feb. 1, 2004 with the title “Rational siRNA design for RNA interference”. 
The conventional practice is to derive specific siRNAs individually for each gene to be inhibited from the sequence thereof. Such a procedure is time-consuming and of low efficiency because the derived siRNAs frequently prove to be unable to inhibit gene expression satisfactorily only when tested. In addition, each individual siRNA sequence entails the risk of having its own nonspecific gene regulation profiles, the so-called off-target effects.
Since the prior art discloses exclusively compositions and methods in which each siRNA is derived individually and in an elaborate manner directly from the gene to be inhibited, the object of the present invention is to make it possible to inhibit simply, efficiently and universally the expression of target genes introduced into the cell by means of RNA interference (“RNAi”).